Magneto ignition circuit



Filed Sept. 7, 1961 R 5 m m w m m m Mn VI R M E H Y B \B United States Patent-O 3,264,520 MAGNETO IGNITION CIRCUIT Henry B. Gersoni, Colliersville, N.Y., assignor to The Bendix Corporation, Sidney, N.Y., a corporation of Delaware Filed Sept. 7, 1961, Ser. No. 136,599 4 Claims. (Cl. 315-218) This invention relates to a novel ignition circuit for internal combustion engines and the like, and particularly relates to a magneto ignition circuit.

The invention has among its objects the provision of a magneto ignition circuit wherein the voltage which the breaker points must interrupt at intermediate and high speeds is markedly reduced.

A further object of the invention resides in the provision of a novel magneto ignition circuit wherein arcing at the breaker points is materially reduced, whereby the 'useful life of the breaker points is very substantially increased.

Another object of the invention is to permit the use of high energy magnetos for obtaining good low speed characteristics without having the usual detrimental effects caused by the production of high voltage outputs at high speeds.

Yet another object of the invention is to provide a novel magneto ignition circuit wherein the period of time required between pulses for the complete dissipation of energy is markedly reduced, so that the magneto may be satisfactorily operated at higher speeds than was formerly possible.

A still further objectof the invention is the provision of a magneto ignition circuit which protects the distributor and other parts of the circuit from insulation breakdown which might occur in the event of an open circuit to the discharge gaps.

Further objects of the invention include the provision of a magneto ignition circuit which permits the use of smaller capacitors to reduce point arcing, the provision of a magneto ignition circuit which permits the satisfactory use of higher acceleration cams even though contact bounce may occur in such installations, and the reduction of energy at the discharge gaps.

The above and further objects and novel features of the invention will more fully appear from the following description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only, and are not intended as a definition of the limits of the invention.

In the drawings, wherein like reference characters refer to like parts throughout the several views,

FIG. 1 is a wiring diagram of a preferred illustrative embodiment of magneto ignition circuit in accordance with the invention; and

FIG. 2 is a graph of voltage output versus speed of rotation of a magneto such as that employed in the circuit of FIG. 1, the graph showing the voltage output of such magneto both with and without the voltage-limiting saturable coil which is an element of the novel combination of the present invention.

In FIG. 1 there is somewhat schematically shown the coil portion of a magneto, the rotatable magnetic fieldproducing element of the magneto being omitted for simplicity. Such portion 10 of the magneto includes a Winding 11. A wire 17 is connected to one end of coil 11. Another wire 16 is connected to the other end of the winding 11. A set of conventional breaker points is connected across wires 16 and 17, as is also an arc-reducing condenser 19.

A wire 20, connected to wire 16, connects the end of "ice the coil 11 to the center contact 21 of a distributor 22. The illustrative ignition circuit is of the so-called low tension type, and so each of the angularly spaced electrodes 25 of the distributor, with which the rotatable distributor finger 24 successively interacts, is connected to its respective discharge gap through a voltage step-up coil. Thus, as shown, each of electrodes 25 is connected to its discharge gap 29 by a wire 26 which leads to the primary of a voltage step-up coil 27. The primary and secondary windings of each coil 27 are connected at one end, the other end of the secondary winding being connected by a wire 30 to one electrode of discharge gap 29. The other electrode of each gap is connected to ground through a wire 31.

The magneto ignition circuit thus far described is conventional. The cam (not shown) for operating breaker points 15 and the distributor arm 24 are connected to the rotatable magnetic field-producing element of the magneto so that the breaker points 15 open to open the magneto circuit at the time that the distributor finger 24 is in position to deliver the voltage thus induced in winding 11 to the proper one of the transformers 27 connected to the discharge gaps 29.

In FIG. 2.the curve designated A is typical of voltage output versus r.p.m. of magnetos such as that employed in ignition circuits such as that described. It will be seen that in curve A the voltage output rises sharply in the r.p.m. range from 0-500, and that the voltage pro- .duced continues to increase in the range from 500-2500 rpm. and above. The high voltage output of such magneto, particularly in the speed range above 500 r.p.m. is unnecessary for proper ignition and is disadvantageous, among other things, in that it produces an unnecessarily high current flow in the transformer.

In accordance with the present invention there is employed a saturable reactor which is connected in the primary circuit in parallel with the breaker points 15. In the illustrative embodiment such reactor takes the form of a coil 32 having a saturable core with substantially square loop characteristics. The core of such coil 32 may, for example, be made of material which is sold commercially under the trade name Toroid Delta-Max. In a circuit similar to that shown in FIG. 1 but with an S-cylinder magneto having an output of 14 kv. at 300 rpm, a typical satisfactory coil 32 has turns of #21 wire wound on a Delta-Max core IT5233. With such coil 32 connected as shown, the output of the magneto, which was the same as that employed in producing curve A, is shown at B. In each case the condenser 19 had a capacity of .74 mfd. Such curve, which is substantially the same as curve A in its initial range, begins appreciably to separate therefrom at a point S and thereafter to lie substantially below curve A, the voltage output increasing with the r.p.m. at a much lower rate in curve B than it does in curve A.

At each cycle of the induction of a voltage in winding 11 the flux in the saturable core of coil 32 increases until it reaches its point of saturation. At such point and beyond it in the same cycle, coil 32 has a very low impedance. When the breaker points 15 open, the voltage across the reactor 32 rises to a predetermined integral value whereat the reactor will saturate. This value will determine the value of the voltage across the secondary windings of coils 27 and thus the voltage at the discharge gaps 29. When saturation of reactor 32 occurs, a short circuit will appear across the breaker points, thus preventing any energy generated by the magneto after the points open to dissipate itself in the secondary circuit. At the lower speeds of the magneto the predetermined value at which the reactor 32 saturates is not reached; therefor it acts as a high impedance path and does not affect the magneto operation at all and will have no adverse efie'cts upon its lowspeed characteristics.

It will be seen that the use of the coil 32 as above described produces a quicker drop otf of voltage upon the condition in the secondary of the voltagestep-up coil 27 might be-harrnful to such coil 27 and to the high tension wiring of the circuit. With the coil 32, however,.most of the energy of the system is, in effect, short-circuited through the coil 32 when its core is saturated so that the I described possible damagecan not occur.

With the ignition circuit of the invention, breaker bounce. is not harmful to the breaker points, because the 'saturable core ofcoil :32 remains saturated, and the circuit, in effect, short-circuited around the breaker points during such bounce. With the circuit of the invention,

.the breaker points can be closed sooner than was forme-rly possible, because the voltage oscillation in thesystern will have died out much more quickly.

is capable of use with the magneto driven at higher speeds than was formerly possible.

Althoughionly one embodiment of the invention has been illustrated in the accompanying'drawings and described in the foregoing specification, it is to be expressly .understood that various changes, such as in the relative dimensions of the parts, materials used, and the like, as

well as the. suggested manner of use of the apparatus of the invention, may be made thereinwithout departing from the spirit and scopeof the invention as will .now be apparenttto those skilled inthe art.

What claimedis:

1. In .a' magneto, I an,inductance winding,' magnetic. means for inducing current flow in said winding, a circuit breaker connected across said Winding, means for, periodically opening and closing saidcircuit breaker; a coil connected in parallel with saidcircuit breaker, and a. saturable core of magnetic material having substantially As above indicated, therefore, the ignition system of the invention.

4 5 square hysteresis loop characteristics onwhich said coil is. wound, said c0il=and core constituting a square loop saturable core reactor which'otfers highimpedance until the core'becomessaturatedwith magnetic .fluxandvery low impedance when the core is saturated, said reactor.

being constructed to become saturated when the voltage across said coil rises. to a predetermined value appreciably higher than the voltage output-ofthe-magneto in a rela'- tively low speed operating range andlower-than the voltageroutput capability. ofthe: magneto in a relatively high speed operating range.

2.? An ignition system for an internal combusion engine comprising a magneto having a primary circuitand ineluding awinding, means for inducing alternatingcurrent flow in said Winding a circuit breaker connected across the winding and means for: periodically, opening and closing saidcircuit breaker, a secondary circuit inductively coupled to said. primary circuit and including a-spark gap, and a saturable' reactor. comprising a winding connected across said {circuit breaker and a saturable core having a square loop hysteresis curve, saidreactor being constructed to saturate after openingof the circuit breaker;

when the voltage induced in the secondary circuit attains a predetermined-value appreciably in excess ofthe volt- "age required to .sparkracross said gap during engine Op ration at minimum speed, whereby saturation of the; core and hence conductivity by said reactor winding does not occur during starting,.andyapredeterminedr appreciable range of low speedengine operation;

3.;An [ignition system as defined in claim 2 ,Iwherein the reactor core is a toroid of magnetic material.

4.:An ignition systemas defined in;claim 2,comprising a step-up transformer havinga primary windin'gin saidfi primary circuit and a secondary windinginsaid secondw, "ary circuit.- a

References Cited ,by the Examiner UNITED 'STATES PATENTS 1/1946 Robinson 315 -218 =X 6/1948 Wall. 315218 JOHN W. HUCKERT; Primary Examiner,

R. 5F. PPOLISSACK, Assistant Examiner. 

1. IN A MAGNETO, AN INDUCTANCE WINDING, A MAGNETIC MEANS FOR INDUCING CURRENT FLOW IN SAID WINDING, A CIRCUIT BREAKER CONNECTED ACROSS SAID WINDING, MEANS FOR PERIODICALLY OPENING AND CLOSING SAID CIRCUIT BREAKER, A COIL CONNECTED IN PARALLEL WITH SAID CIRCUIT BREAKER, AND A SATURABLE CORE OF MAGNETIC MATERIAL HAVING SUBSTANTIALLY SQUARE HYSTERESIS LOOP CHARACTERISTICS ON WHICH SAID COIL IS WOUND, SAID COIL AND CORE CONSTITUTING A SQUARE LOOP SATURABLE CORE REACTOR WHICH OFFERS HIGH IMPEDANCE UNTIL THE CORE BECOMES SATURATED WITH MAGNETIC FLUX AND VERY LOW IMPEDANCE WHEN THE CORE IS SATURATED, SAID REACTOR BEING CONSTRUCTED TO BECOME SATURATED WHEN THE VOLTAGE ACROSS SAID COIL RISES TO A PREDETERMINED VALUE APPRECIABLY HIGHER THAN THE VOLTAGE OUTPUT OF THE MAGNETO IN A RELATIVELY LOW SPEED OPERATING RANGE AND LOWER THAN THE VOLTAGE OUTPUT CAPABILITY OF THE MAGNETO IN A RELATIVELY HIGH SPEED OPERATING RANGE. 